[root shadowfax ~]# e2fsck -f -n /dev/loop7
e2fsck 1.39 (29-May-2006)
Group descriptors look bad... trying backup blocks...
e2fsck: Bad magic number in super-block while trying to open /dev/loop7
The superblock could not be read or does not describe a correct ext2
filesystem. If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
e2fsck -b 8193 <device>

Did you try one the alternatae superblocks? (mkfs.ext3 -n might help)
Last time I myself had to use this it did not work. So I'm really curious
if e2fsck -b actually works when this message appears.
Christian.
--
BOFH excuse #78:
Yes, yes, its called a design limitation